When it comes to hydration, women face unique challenges that fluctuate with the menstrual cycle. The complex interplay between estrogen and progesterone, two key sex hormones, has a profound effect on fluid balance, particularly in the second half of the cycle. Understanding these dynamics is essential for maintaining optimal hydration, performance, and overall health.
How Hormones Influence Fluid Balance
Estrogen and progesterone not only regulate reproductive functions but also play a critical role in fluid dynamics. Estrogen, in particular, influences plasma volume (PV), the amount of fluid within the blood vessels. During the pre-ovulatory phase, when estrogen levels are high, PV reaches its peak. However, as women transition into the mid-luteal phase, progesterone becomes dominant, and plasma volume can drop by as much as 8%. This reduction in PV occurs because fluid and proteins move out of the bloodstream and into the spaces between cells—a process influenced by hormonal shifts.
The Impact on Hydration in the Second Half of the Cycle
As plasma volume decreases during the mid-luteal phase, maintaining adequate hydration becomes increasingly important. Not only is there less fluid within the bloodstream, but hormonal changes also affect how your body regulates water and sodium. This can lead to an increased risk of dehydration, particularly in the heat, as the body’s ability to manage temperature and fluid balance becomes compromised. This becomes particularly important if you live in Austin and exercise in the summer months. Figuring out how to “sodium load” through drinking broths the night before can impact exercise capacity and optimise your workouts during the luteal phase of your cycles.
Menstrual Cycle and Thermoregulation
One of the lesser-known effects of the menstrual cycle on hydration is how it alters thermoregulation—the body’s ability to maintain its core temperature. During the two weeks prior to your menses, baseline core temperature is reset to a higher level, and the onset of sweating is delayed. This means that during exercise, especially in hot climates, it may take longer for the body to start cooling itself down, increasing the risk of overheating. One way to manipulate is to wear light clothing when exercising, especially if you know that you will be outdoors in the heat. If you are going to be exercising more than 2-3 hours, using a glucose snack can be optimal which can help support sodium absorption in the bloodstream.
Additionally, during this phase, the sensitivity of the blood vessels in the skin decreases, which slows down vasodilation—the process by which blood vessels expand to release heat. These changes can reduce exercise capacity, especially in high temperatures, and may make women more prone to dehydration during the second half of their menstrual cycle.
Practical Hydration Strategies Across the Cycle
Given the unique fluid shifts during the menstrual cycle, women should tailor their hydration strategies to these hormonal changes:
1. Pre-ovulatory Phase (Days 1-14): Estrogen is on the rise, and plasma volume is at its highest. During this phase, women may not need to increase their fluid intake as much since the body’s fluid balance is more stable.
2. Mid-Luteal Phase (Days 15-28): As plasma volume drops and thermoregulatory responses shift, it’s important to be more mindful of hydration. Drink water more consistently throughout the day, and consider increasing electrolyte intake—especially if you’re exercising or spending time in the heat.
3. Exercise Hydration: Women who exercise, particularly in warmer climates, should ensure they’re hydrating before, during, and after workouts. Water alone may not be enough—electrolytes are essential to maintain the body’s sodium balance and prevent dehydration. We don’t need electrolytes all year long, but it is particularly important to know when they can be useful and how to adequately use them.